Gardner-Rasheed feline sarcoma virus (GR-FeSV) is an acute transforming retrovirus which encodes a gag-onc polyprotein possessing an associated tyrosine kinase activity. The integrated form of this virus has been isolated in the Charon 21A strain of bacteriophage lambda, and demonstrated ability to transform NIH/3T3 cells at high efficiency upon transfection. Foci induced by GR-FeSv DNA contained rescuable sarcoma virus and expressed GR-P70, the major GR-FeSV translational product. Localization of long terminal repeats with the DNA clone made it possible to establish the length of the GR-FeSV at 4.6 kbp. Analysis of heteroduplexes formed between lambda-FeLV and lambda-GR-FeSV revealed the presence of a 1.7-kbp FeLV unrelated segment designated v-fgr. This region was sufficient in size to encode a protein with similar molecular weight of GR-P70.